Question is ⇒ Stability of a synchronous machine, Options are ⇒ (A) decreases with increase in its excitation, (B) increases with increase in its excitation, (C) remains unaffected with increase in excitation, (D) any of the above, (E) , Leave your comments or Download question paper.

Question is ⇒ Stability of a synchronous machine, Options are ⇒ (A) decreases with increase in its excitation, (B) increases with increase in its excitation, (C) remains unaffected with increase in excitation, (D) any of the above, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	Stability of a synchronous machine
A.	decreases with increase in its excitation [Wrong Answer]
B.	increases with increase in its excitation [Correct Answer]
C.	remains unaffected with increase in excitation [Wrong Answer]
D.	any of the above [Wrong Answer]
View Answer 8 -5 Explanation:- Answer : B Discuss it below : !! OOPS Login [Click here] is required to post your answer/result Help other students, write article, leave your comments

Previous question Next question

Also Read Similar Questions Below :

⇒ The power developed by a synchronous motor will be maximum when the load angle is
zero
45°
90°
120°

⇒ An over-excited synchronous motor is used for
fluctuating loads
variable speed loads
low torque loads
power factor corrections

⇒ The standard full-load power factor ratings for synchronous motors are
zero or 0.8 leading
unity or 0.8 lagging
unity or 0.8 leading
unity or zero

⇒ Which of the following methods is used to start a synchronous motor ?
Damper winding
Star-delta starter
Damper winding in conjunction with star-delta starter
Resistance starter in the armature circuit

⇒ Hunting in a synchronous motor cannot be due to
windage friction
variable load
variable frequency
variable supply voltage

⇒ Armature of a synchronous machine is kept fixed because
of reducing number of slip rings on the rotor
armature is associated with large power as compared to the field circuits
of difficulty of providing high voltage insulation on rotor
all of the above reasons

⇒ Power factor of a synchronous motor is unity when
the armature current is maximum
the armature current is minimum
the armature current is zero
none of the above

⇒ The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motor running at full load, is of the order of
zero degree
two degrees
five degrees
ten degrees

⇒ For V-curves for a synchronous motor the graph is drawn between
field current and armature current
terminal voltage and load factor
power factor and field current
armature current and power factor

⇒ The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as
locked-rotor torque
synchronous torque
pull up torque
reluctance torque

⇒ In a 3-phase synchronous motor, the negative phase sequence exists when the motor is
supplied with unbalanced voltage
under-loaded
over-loaded
none of the above

⇒ Dust and dirt accumulation on motor winding will result in
rise in winding temperature
increased core losses
shorting of coils
eddy current flow

⇒ The operating speed of a synchtunous motor can be changed to new fixed value by
changing the load
changing the supply voltage
changing frequency
using brakes

⇒ In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be
3000 r.p.m.
1500 r.p.m.
750 r.p.m.
none of the above

⇒ The armature current of the synchronous motor has higher values for
high excitation only
low excitation only
both (a) and (b)
none of the above

⇒ If one-phase of a 3-phase synchronous motor is short-circuited, motor
will refuse to start
will overheat in spots
will not come upto speed
will fail to pull into step

⇒ A synchronous motor can operate at
lagging power factor only
leading power factor only
unity power factor only
lagging, leading and unity power factors

⇒ A three-phase synchronous motor will have
no slip-rings
one slip-ring
two slip-rings
three slip-rings

⇒ Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current ?
High field current
Low short circuit ratio
High core losses
Low field current

⇒ Mostly, synchronous motors are of
alternator type machines
induction type machines
salient pole type machines
smooth cylindrical type machines

⇒ If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to
increase in both armature current and power factor angle
increase in back e.m.f. but decrease in armature current
increase in both armature current and power factor which is lagging
increase in torque angle but decrease in back e.m.f.

⇒ Which of the following motors will be used in electric clocks ?
D.C. shunt motor
D.C. series motor
A.C. induction motor
A.C. synchronous motor

⇒ The armature current of the synchronous motor
has large values for low excitation only
has large values for high excitation only
has large values for low and high excitation
any of the above

⇒ In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on
d.c. excitation only
speed of the motor
load on the motor
both the speed and rotor flux

⇒ A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will
remain same
go down
improve
none of the above

⇒ A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because
synchronous motor has no slip
stator supply is not required to produce magnetic field
mechanical load on the rotor remains constant
synchronous motor has large airgap

⇒ In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately
one-third
twice
thrice
six times

⇒ The efficiency of a properly designed synchronous motor will usually fall in range
60 to 70%
75 to 80%
85 to 95%
99 to 99.5%

⇒ By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?
By changing the supply frequency
By interchanging any two phases
By changing the applied voltage
By changing the load.

⇒ Which of the following motors is nonself starting ?
D.C. series motor
synchronous motor
Squirrel cage induction motor
Wound round induction motor